It's becoming more and more common to use VPNs online. They can help protect your identity, can help protect you from attackers, and can allow you to access region restricted content. It's not just businesses and pirates, regular everyday people are starting to use them more too.
Many websites depend on ad revenues, but lots of traffic coming from the same IP may be of little value to ad providers. Some ad providers will only count a given IP once per day. This means that as more users of a given website switch to VPNs, the site may have lower revenues, despite getting the same amount of traffic. While rare, a few sites have started combating this by blocking visitors who are using a known proxy or VPN IP address. This is irritating, but it does make sense. Your ad views pay for their site, but this only works if your view has value, and if you're using a VPN, your view may not.